1. Field of the Invention
The invention concerns an axial and radial holding assembly for the rotor blade of a turbojet engine able to prevent hammering of the blade feet and the groove, and more particularly a block that can be housed between the blade foot and the bottom of the groove provided in the rim of the rotor disk.
2. Description of the Prior Art
Axial and radial holding assemblies for blades, such as that described in French Pat. No. 2 345 605, consisting of a block that is placed between the blade foot and the bottom of the groove so as to hold the upper part of the blade foot dovetailed against the side teeth of the groove, with the block being held axially by a U-shaped lock cooperating with corresponding notches provided in the blade foot and in the teeth of the groove, are well-known and the system shown therein is simple and effective. To facilitate or even make possible the assembly and dismantling of the unit, there nonetheless is some play between the block, the blade foot and the bottom of the groove (at least for most blades). This play proves to be harmful from the viewpoint of wear. Indeed, during self-rotation or low-speed rotation of the rotor, the centrifugal force exerted on the blades is no longer sufficient to keep the blade feet pressed against both oblique faces of the grooves.
With each turn, the blades go from a position of resting on one side of the seating to a position of resting on the other side. This produces chatter and, what is more serious, hammering, which does serious damage to the surfaces in contact with one another. If such hammering is difficult to accept even for parts that are easily replaceable, such as the blocks or even the blades, it is impossible for the rotor disk, for which such damage is entirely unacceptable.
Hence, French Pat. Nos. 2 300 215 and 2 426 151 offer solutions that make use of blocks having an elastic part able to maintain permanent contact between the blade foot and the groove. The block described in the first patent cited consists of three lengthwise, independent parts, two lateral parts, and one central part. The two lateral parts have on the ends of two adjacent faces a plurality of flanges provided so as to be able to press against the front or rear face of the disk, on either side of the groove and against the radial ends of the blade feet. These two symmetrical parts are introduced into the space between the blade foot and the bottom of the groove and are held apart by the central part having a shape approximately complementary to the remaining space. This part includes a housing that receives an elastic member resting against the bottom of the groove. The three parts are unitarily connected with a bolt after being put in place.
The second patent cited describes a block having two lateral parts identical to those of the preceding patent, but a central part consisting of two elements and a supplementary locking block. One of the elements forms a spacing block that can be elastically distorted in the axial plane and cooperates with a groove provided in the small bar forming the other element and is intended to be placed against the bottom of the groove. Installation of the system is achieved as in the previous case by introducing the lateral parts, the small bar, and then the spacing block. Then the locking block is placed between the ends of the small bar and the spacing block and this presses the spacing block against the small bar and the blade feet. A bolt holds the various parts together and assures locking engagement therebetween.
The elastic distortion of the spacing block, when it is in place, develops sufficient contact strength to hold the blade foot regardless of the rotor's rotation speed. The large number of parts in either of these solutions from the prior art nonetheless makes assembly and dismantling of the blades a delicate task.